Initial timing acquisition is fundamental in a baseband wireless modem design to enable a receiver of a modulated signal to know which part of the signal constitutes the data payload, so that valid data may be properly extracted from the signal. In many wireless communication standards, such as the IEEE 802.15.4 (ZigBee) standard, a synchronization header (SHR) including a preamble and a start frame delimiter (SFD) sequence is generally included at the beginning of the physical specification (PHY) packets containing the data. For example, according to the ZigBee standard, the preamble may include eight repetitions of a particular preamble pattern followed by the SFD, which indicates the end of the SHR and the start of the packet data. The receiver knows the preamble and exploits this knowledge to provide accurate synchronization information to all baseband modem blocks, such as a data demodulator.
Conventional techniques for initial timing acquisition, however, generally have several drawbacks. One drawback is that conventional techniques tend to require full preamble detection. Full preamble detection relies on detecting all peaks by correlating expected patterns, such as by a threshold-passing correlation-based method. This means that a high quality signal would be required during all expected preamble repetitions (≈128 μsec for the ZigBee standard). Detecting a lesser number of repetitions may not provide timing information, and reducing detection threshold may increase chances of false-alarms. Thus, conventional techniques that require full preamble detection may be vulnerable to noise, front-end settling and delay in preamble search.
Another drawback of the conventional techniques is that preamble detection and SFD detection are often implemented as two separate hardware mechanisms. For example, after detecting the requisite number of consecutive preamble repetitions by one hardware mechanism, another correlation-based hardware mechanism would attempt SFD detection. Separate detectors for preamble detection and SFD detection may significantly increase the amount and complexity of the receiver's hardware.